In the air conditioning and heating of commercial buildings, water source heat pumps are effective devices for maintaining the desired temperature conditions throughout the building. Each area of the building will be conditioned by a separate heat pump, but all heat pumps are connected in a single water loop.
Even in the dead of winter, the presence of occupants and equipment, such as lights and typewriters, will often provide all the heat necessary to condition the building. However, areas near windows will require a greater portion of the heat to remain at the desired temperature, while core areas of the building may well need to have heat removed. The water source heat pumps satisfy this requirement by taking heat from the core areas and redistributing the heat through this continuous water loop to the heat pumps in the outside areas. Thus, the proper environmental conditions can often be maintained in the building for very low costs by simply transferring excess heat from one area to an area which requires supplemental heat.
Each water source heat pump contains a compressor run from an electrical power source. Safety monitoring circuits are required to insure that the compressor will be stopped if the heat pump malfunctions. For example, the compressed fluid may exceed a desired pressure or fall below a desired minimum temperature. Whatever the malfunction condition, the compressor must be disconnected from its power source and kept disconnected until repair personnel can determine the cause of the defect.
In order to satisfy these requirements, expensive conventional electromechanical relays have been used to lock out the compressor when a safety function is sensed. Such relays require a special matching circuit and special compressor contacts on the compressor, providing an expensive package. A need thus exists for a less expensive circuit for performing this function.